Such a hose pump is described in German OS No. 2 140 872 published Feb. 22, 1973 and is used mainly for conveying of concrete. The efficiency of the pump and a damage of the conveying hose by stones present in the concrete are to be avoided in this hose pump by a special drive of the pinch rollers through frictional resistance and by providing an elastic outer layer on the pinch rollers for which purpose a complicated connecting bracket is used.
This connecting bracket is not absolutely needed particularly when using such a hose pump to convey liquids. It increases in this case merely the weight and the energy requirements of the entire pump. Compared with this, the drive of the pinch rollers through frictional resistance is particularly advantageous. On the one hand, the frictional force is, even at a high bearing force urging the pinch rollers against the rolling surface, very poor due to the pure rolling movement but, on the other hand, it permits an entirely jerk-free operation of the hose pump.
In the case of a rigid construction of the pinch rollers, the drive member and the rolling surfaces, a drive through frictional forces would require a high degree of manufacturing precision in the just mentioned structural parts. For this reason, the rigid pinch rollers of the known hose pump have an elastic outer layer which is provided to assure a frictional force between the drive member and the pinch rollers. However, such an elastic outer layer on the pinch rollers for transmission of the rolling movement from the drive member to the pinch rollers is of a disadvantage in many cases. In particular, when the hose pump stands still for a longer period of time, there exists the danger that the elastic outer layer is deformed by the constant pressure on the drive member, the rolling surface and the conveying hose or these parts adhere to one another or both occur together. Starting of the pump requires then particularly large forces which often can no longer be produced by the drive motors.
If the deformation does not disappear through the rolling movement, a constant jerklike conveying of the conveyed medium, an increased energy consumption and a strong stress on the conveying hose will take place.
Therefore, the purpose of the invention is to simplify the design of a hose pump pinch rollers driven by frictional resistance and to increase their reliability, in particular for an unsupervised long-time operation with stand still phases.
This purpose is attained intentively by the pinch rollers being constructed as resilient hollow cylinders.
It is of a particular advantage if the pinch rollers are made of a hard-elastic material, in particular of spring steel and if the outer diameter of the pinch rollers is greater than the radial spacing between the rolling surfaces of the housing and the drive member.
The inventively constructed pinch rollers are no longer flattened, as this is the case in known pinch rollers, at the contact points with the drive member and the rolling surfaces, but are almost of a circular or elliptic shape. The angles which are enclosed at the contact points between the pinch rollers and the rolling surfaces are consequently substantially smaller (near zero) in the case of the inventive pinch rollers than in the known design. The starting forces of the inventive hose pump are correspondingly small. The pressure which is needed for the frictional resistance between the driving and the driven parts is not affected, as exists with a soft, elastic outer layer on the pinch rollers, through the inventive design of the pinch rollers as resilient hollow cylinders. The pinch rollers may therefore be made of a very hard material, as for example spring steel so that the portion of the driving energy, which portion is consumed otherwise by the pressing operation in the elastic material, can be saved. Such materials have additionally the advantage that they, even after longer stand still time for the hose pump, do not permanently deform or adhere to the contacting parts.
The pinch rollers can, depending on the size of the hose pump and depending on the required number of the pinch rollers, be distributed either in close arrangement or separated from one another by a cage enclosing same around the drive member.
In particular, if a cage is not needed, it is advantageous if the drive member has two flanges which center the pinch rollers and limit their axial movability from both sides.
In order to utilize as much as possible the advantages for a jerk-free, even conveying output from the hose pump, which advantages are caused by the inventive construction of the pinch rollers, it is particularly advantageous if the inner wall of the annular groove is eccentric with respect to the rolling surface. The conveying hose is then not suddenly squeezed or released upon engagement with or release of the pinch rollers; these operations pass continuously over into one another in such a further development of the inventive hose pump so that periodic variations of the conveyor output can hardly be observed any longer. This can be of importance for a precise measuring in particular by using the hose pump for physical, chemical, medical or biological experiments-- for example electrophoretic separating methods. To a particular (special degree) degree this is true for the use of such pumps in space flight experiments.